The present invention relates to a circuit arrangement for preheating electrodes of a discharge lamp connected in series with a ballast by means of a supply voltage of alternating polarity, comprising
a branch A for connection to the electrodes of the discharge lamp, which branch A comprises a switching element, PA1 a control circuit coupled to a control electrode of the switching element for generating a control signal to render the switching element conducting during preheating in each cycle of the supply voltage, PA1 a circuit portion I coupled to the control circuit for influencing the control signal in dependence on whether the ballast is inductive or capacitive.
Such a circuit arrangement is known from Netherlands Patent Application 159853 laid open to public inspection. In the known circuit arrangement, the circuit portion I comprises a branch which includes a transistor. The control signal is influenced in that this transistor becomes conducting exclusively if the ballast is capacitive. It is realised by means of this branch that instability in the operation of the circuit arrangement in the case of a capacitive ballast is avoided. The known circuit arrangement can accordingly be used in combination with both inductive ballasts and capacitive ballasts. A disadvantage of the known circuit arrangement, however, is that the effective value of the current through branch A, with which the lamp electrodes are preheated, is comparatively low. The result of this is that it takes a comparatively long time before the electrodes of the discharge lamp have reached a temperature at which a sufficient emission of electrons occurs for igniting the discharge lamp at the given ignition voltage. This comparatively long preheating time is felt to be inconvenient by users.